Abrasive articles



Patented May 12, 1 953 Norman P. Robie, Hamburg, .N. .Y., assignortoElectro Refractories & Abrasives Corporation, a

. corporation of Delaware N Drawing. Application August 10, 1949,

:SerialNo.109',621;

60laims. (01. 51-298),

. This inventionrelates to abrasivearticlesand more particularly togrinding wheels ;bonded with thermo-setting resin. -A primary objectofmy'invention is to produce abrasive bodies withsuperior cutting ability,which maybe-measured either in terms of away very rapidly. I have foundthat by the use of my invention it is possible to makethe work done perbody during the useful lifeof the same; or in terms of rateofcut.Another'obj'ect is to provide an abrasive wheel whichis cooler duringcutting "than the usual wheels;particu-' larly thosebondedwithjsyntheticresins capable ofhighspeed operation.- {Another -objectisto increase the safety factor byreducin the tendency tobreak when theWheel is used in severecutting applications. i

"My invention residesparticularly in the use of certain fillers which Ihave found it advantageous to incorporate inthe mixfrom' which the'bodyor'wheel ismade; Thesefillers are not in themselvesabra sives in the'usual'sense, but greatly improve'the performance of the body. or wheelwhen it is in operation by modifyingand/cr extending the binder usedtherein. The use of fillers in such wheels is old in the"art,'the use ofsuch materials'as' cryolite, clay, fine alumina, lead oxide, flint,rouge, lime or magnesium oxide having been described in patents orpracticed more or less widely-in the industryw In some cases theselection of these, materials has been to secure some chemical reactionwith the resin or with the water vapor released during thecur ingoperation. The use of lubricating fillers such as graphite has also beensuggested. The .fillers according to my' invention; are

chemicallyinert and do not possess the quality. of lubricity, hence theyseem to fall into-a different category from theforegoingi My fillers-incommon with some of the others, seem'to make. the abrasive articles orwheels containin them'somewhat denser and harder-than' whenthe fillersare left. out, -but theyvary sharply from a e e er e wheel ,orthe.metalsothat the wheel binds in the slot being cut, with the re-- sultthat thewheel. seizes. and breaks. Further,

ifexcessive heat is generated, the bond disintegrates, causing chips tobreak out of the wheel edge. To avoid. these difficulties, such wheelswheels far stronger and more solid, and yet not secure excessive heatingeven when metal is removed-at a rapid rate. While my invention is highlyapplicable to cutoff wheels, it is not limited tothem, but is ratherapplicable to resin bonded wheels and abrasive articles of all sorts.

I have found that certainlead salts which are not reactive withphenolicresins and do not form lead phenolates, as'do those suggested byKuz'mick in U. S. Patent #2,083,719, are un usually valuable fillers inphenolic resin bonded abrasives. These salts are the substantiallyinsoluble and anhydrous lead salts of strong acids, includingspecifically lead chloride, lead fluoride, lead sulfate, leadflue-chloride and the like. I do not know why these fillers are sosuperior, but I have established by repeated tests in the laboratory andin the field that such is the case. I also know that they do notembrittle the resin by reaction therewith, as do oxidic compoulnds oflead. I

In the manufacture of abrasive articles in accordance with my invention,I have used my fillers in various amounts from as low as 3% of the mixby weight to as high as 30%. I prefer, however, to use from 10 to 25%with 20% as generally satisfactory.

.The abrasive employed may be of any desired-- type, such as aluminumoxide, corundum, emery,

diamonds. and the like. The binder may be of any thermo-setting resin ofthe type commonly used as binders in the abrasive industry such, forexample, as phenolic or alkyd resins.

" fusible and soluble, heat reactive, heat hardening containingare.often maderelatively open or porous, which 1 Me a er e r r ur ththey ea phenol-formaldehyde resin capable of heat hardening into aninfusible, insoluble state. The phenol-formaldehyde resin is a two stageresin usually hexamethylenetetramine groundthereinto act as a hardeningagent.

Preferably I use a plasticizer, which may be a solvent, a liquid resinor a solution of resin in accordance with the well known practice in theabrasive industry. The following maybe em--,

ployed'; cresol, furfuryl alcohol, furfural, liquid phenolic resins.

These materials are thoroughly mixed according to conventional practiceand formed into. articles of desired shapes by either hot or cold beheated OroVen-baked in the usual manner to thermo -set the bond.

; In orderthat the method of manufacture may I preferably employ afinely powdered, less than 1% on mesh, less'than'15% on 325 mesh,initially be clearly understood, I give the following examples by Way ofillustration and not limitation:

Example I 200 gra rnsof technical grade, finelyv powdered lead chlorideis first mixed dry with 110 grams of powdered phenol formaldehyde resinof the A stage heat reactive variety (sold by the Var; cum ChemicalCorporation under the number V1364). In a separate container I mixtogether 690 grams of fused aluminum; oxide abrasive grains using equalamounts of" grits 24; 3.0 andz36..

respectively. After these are well mixed, they are wet up with 8 cc. ofcresolr and the mixture,

of powdered bond and filler is then added and thoroughly mixed in. Thematerial thus prepared is then placed in a mold, levelled and Example IIAzwheelin whichsiliconcarbide is used as the abrasivemay be made byemploying the iollovh ing pe'rcentages of ingredients by weight:

"'S ilicpnfcarbide grain 64.4%. The grain may befir'ithe and 36' grainsize, and preferablyequal'quantities of each size are used.

"Thib ondin g agz'ent may be the same asspecified 'in- Example I, andconstitutes 12.6% of the finalprodiict.

Ladsulfate in powdered form is employed to the extent er -"2 of theweight of the final product The silicon carbide grain is wetted with asuitable plasticizer, for example 30 cc. oi cresol per poundor resinbond'use'd, before mixing with the leadsulfate filler'and' the resinpowders, The material is'then molded to a density oiabout.9891"pound"per cubic inch and may then be cured or baked asdesci'ibedin Exarnple'l.

The specific examples I have-given have been concer-nedchi'efly withcutoff wheels because due to their thinness, these can he tested withmininiuni requirement formaterial. I do not confine useo'f myfillers'to-such wheelshowever, but may use "them in portable wheels,snagging wheels, thread grinding wheels, or any other. type of abrasivein which synthetic resin bonds are-used. Their use in wheelscontainingnatural' on synthetic rubber in the bond is beneficial. The

fillers-may he used with any of the common types of abrasive includingalumina or silicon carbide, and with' phenolic, alkyd or otherthermosetting 1'esin's. Their use" is beneficial without regard to thetype of plasticizer used. The Wheelsmay be made by either hot or coldpressing methods.

I mayadmix my fillers with other cheaper fillers,such as cryolite-orlime in order to extend their utility,'or I may use them unmixed. Ihave; in' general used them in powder form; such that 100% will passthrough a 325 mesh sieve, but

their beneficial effect-is not primarily dependent upon size solong asthey are 'of the order of fineness of 100' mesh or less.

In azseriesof comparative tests, I made wheels identical with oneanother except for. the filler used, as follows: a mix was made from 79%by weight of fused alumina grain comprising equal proportionsof. 24, 30and 3 6'grit. This grain was wet up with a plasticizer in the usual wayand a premixed lot of powder consisting of 14.2% by weight of reactiveheat-hardenable phenolic resin, 5.9% filler and 0.87% lime was thenmixed in and-the mi-xformed into-wheels having a density of 0.0866 poundpericubic inch. These wheels were then baked between batts, theirtemperature being raised to 360 F. and held at that temperature for overnine hours. The wheels. each of which was 16 x x 1 inches were thenused. to, ma l ;e 25.. cuts through a 1 inch bar of eold rglled steeland the loss of abrasive determined-byweighing; the wheel before andafter use. My, leadfluoride filler gave superior results as followsGrams Wheel Loss Filler Potassium 1110.

The other fillers. here chosen are those commonly used in suchabrasivearticles, It islinown that theireiiectivenss. decreases, as thepercentage fallsbelowthat use.d,,soth at.if for instance the volume ofthe cryolite and fiuoboratehad been. assrnall as the volumeofthe muchdenser lead salt, the results would have been even. more favorable to.my material.

In another. series, of. compaa ative. tests made with my fillers incomparison withlitharge, 69% weight ofiused aluminagrain, sized. asabove. was similarly ,madeup into wheels using 11%. of. powderedr,esin.and.20% by Weight of filler. The wheels. in this case. wereeach'pressedto a density. of. 0.11.1oound per. cubicjinch Afterfbaking,they were. eachused tomake tencuts through 1 inch stainlesssteel rodsand the. lossfo f weight of, each wheel measuredasbefore, The resultsare ive b ow Grams Filler Wheel Loss Load'cliloride, C. P 1 l0 1 eadchloride, techn 9 Lead sulfate, 0. P 10. 5 Lithargeftechnia l8. 5Basicload sulfate 1 S 19 sta e at tests were: madeunder. drastic test,conditiens in which. it was-attempted. to. u -slic s fr m a. tou h our.inch square stainless steel bar. The wheels; madefwithaconvens el fi ersmade nly; partial cuts. and: then,

beeau of thetremendous heatgenerated; seized:- crumbled and brokerWith-.wheelsrmade.

5 usinsmyleacl c lfl de and: lead. sulfate fillers se-made Sui-le t bash ir h q -lawms table,

Grams Wheel- Loss oratory results, with superiority in pieces proc-.essed per wheel running 50% above normal in many instances.

Having thus described my invention in general terms and given a specificexample of its application, I desire patent protection within the scopeof the following claims:

1. A cutoff wheel comprising abrasive grains, from to 25% by Weight ofan anhydrous lead salt of a strong acid selected from a group consistingof non-basic lead sulfate, a lead halide and mixtures thereof, and athermo-set phenolic resin bond uniting said grains and said lead saltinto an integral body, said lead salt being substantially insoluble inwater and non-reactive with said bond and being substantially uniformlydispersed throughout said body.

2. As an intermediate article of manufacture, a shaped object for themanufacture of an abrasive body therefrom, said shaped object consistingof a compacted formed mixture of abrasive granules, a thermal settingphenol formaldehyde resin, and from 3% to 30% by weight of a finelydivided lead salt of a strong acid, said salt being substantiallyinsoluble in water and non-reactive With said bond and being a member ofthe group of compounds consisting of non-basic lead sulfate, leadhalides and mixtures thereof.

3. An abrasive article comprising abrasive grains, an anhydrous leadsalt of a strong acid in finely divided form, said salt being a memberof the group consisting of non-basic lead sulfate, lead halides andmixtures thereof, and a phenoli resin thermo-set bond uniting saidgrains and said lead salt into an integral body, said lead salt beingsubstantially insoluble in water and nonreactive With said bond andbeing substantially uniformly dispersed throughout said body, said leadsalt comprising from 3% to 30% by weight of the article.

4. An abrasive article comprising abrasive grains, an anhydrous leadsalt of a strong acid in finely divided form, said salt being a memberof the group consisting of non-basic lead sulfate, lead halides andmixtures thereof, and a phenolic resin thermo-set bond uniting saidgrains and said lead salt into an integral body, said lead salt beingsubstantially insoluble in water and nonreactive with said bond andbeing substantially uniformly dispersed throughout said body, lead saltcomprising from 10% to 25% by weight of the article.

5. An abrasive article comprising abrasive grains, from 3% to 30% byweight of a lead halide in finely divided form and a phenolic resinthermo-set bond uniting said grains and said lead salt into an integralbody, the lead salt being substantially uniformly dispersed throughoutsaid body.

6. An abrasive article comprising abrasive grains, from 3% to 30% byweight of a non-basic lead sulfate in finely divided form and a phenolicresin thermo-set bond uniting said grains and said lead salt into anintegral body, the lead salt being substantially uniformly dispersedthrough out said body.

NORMAN P. ROBIE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,083,719 Kuzmick et al. s June 15, 1937 2,273,891 Pollak etal Feb. 24, 1942 2,456,920 Coes Dec. 21, 1948

3. AN ABRASIVE ARTICLE COMPRISING ABRASIVE GRAINS, AN ANHYDROUS LEADSALT OF A STRONG ACID IN FINELY DIVIDED FORM, SAID SALT BEING A MEMBEROF THE GROUP CONSISTING OF NON-BASIC LEAD SULFATE, LEAD HALIDES ANDMIXTURES THEREOF, AND A PHENOLIC RESIN THERMO-SET BOND UNITING SAIDGRAINS AND SAID LEAD SALT INTO AN INTEGRAL BODY, SAID LEAD SALT BEINGSUBSTANTIALLY INSOLUBLE IN WATER AND NONREACTIVE WITH SAID BOND ANDBEING SUBSTANTIALLY UNIFORMLY DISPERSED THROUGHOUT SAID BODY, SAID LEADSALT COMPRISING FROM 3% TO 30% BY WEIGHT OF THE ARTICLE.